You know, it's true that demons are nowhere near as commonly encountered as they were, say 200 years ago. And I do believe a lot of this stems off of the consciousness shift humanity has undergone since then. It's not that demons aren't real (they are) and humanity is slowly waking up to this fact; the truth is that the belief in the supernatural have gravely diminished over the past hundred years because of the conditioning social media plays on the mindset of normal people and the fact that science chooses not to accept these things because it can't be replicated in a laboratory, and because the funding for this type of research is never granted. People who donate money to research have a choice on where that money goes to and by extension, the results the turn up.

If you want to go back a few thousand years or so you'll find that humanity's connection with nature and the spiritual realm is far greater than it is today. Only under certain conditions were humans able to communicate with spiritual beings and elementals. This knowledge wasn't widely known by everybody, but mainly the priestly class of the ancient druids, magi and sages. They preserved this knowledge because under the wrong hands it could be dangerous.

Then Christianity happened. As much as the Roman Emperors tried to squash this religion in its infancy, the sacrifice of one man revolutionized the way everyone viewed themselves and the world. Something greater than ourselves awaits after death! Eventually the belief grew so great it could not be contained, so it had to be controlled. The belief in a new savior was put forward and mind games were played to "win over" followers. Any deity with a depiction of horns was cast down as evil, while Christianity unwittingly adopted various pagan beliefs along the way. A few hundred years and the Catholics were in power and attacking rival religions. After milking the minds and stealing the wisdom of those druids in the Celtic Isles and later the Shamans of South America, they killed their people and destroyed their cultures.
After Rome fell and the Church remained, the Pope took the liberty of crowning new kings all over Europe, all the while setting up witch hunts against any and all heretics, eliminating rival religions such as the Cathars and Bogamils, stealing what sacred knowledge remained in the hands of the few.
Some groups were able to preserve this knowledge and remain hidden underground for centuries. Most predominantly, the Knights Templars, who were once sworn to uphold the Church. They began to collect this knowledge from ancient Jewish scrolls and traded knowledge with their friends/enemies, the Muslim Hashashins (Much like the CIA/KGB exchange intel today. The Church eventually betrayed the Templars. The survivors set up underground lodges or secret societies that would emerge 400 years later as the Freemasons.

During the centuries of Catholic reign exorcisms have taken place in greater numbers then there are today (or at least greater than that which is reported today). The secret societies in the 1700's started reintroducing the occult sciences to the people during the Renaissance after the Church had lost its Inquisition powers and was weakened by the Wars of Religion. Practicing the Rite the contact extradimensional beings (angels and demons) known as the Rite of Strict Observance, which was deemed too dangerous by Freemasons, Martinists and the Illuminati in 1782 at the Congress of Wilhelmsbad. None were allowed to practice it without the authorization of "Unknown Superiors." But there have been occultists appearing throughout history, reading ancient books and finding ways to open the window to the spiritual realm and call forth demons and various spirits. See Johanna Faustus, John Dee, Eliphas Levi, MacGregor Mathers, Aleister Crowley, etc.

Not all methods from connection with the other side have been eradicated, Ouija boards, seances and table turnings still sometimes occur today. But the connection with the other side has grown weaker as those who attempt to make contact must believe in it as well. There is energy in the human belief that makes the demon more attractive. Most times they will not or cannot appear physically because they have no physical bodies to inhabit... this is also why channeling them is so dangerous, in having no body to interact with this world they will try to take one from whomever opened the window.

Several long forgotten books have found there way back into book stores such as Amazon.com relaying ancient symbols used to conjure demons and such in old Grimoires such as The Key of Solomon under the New Age belief.